Priority is claimed to Korean Patent Application No. 00-13039 filed on Mar. 15, 2000, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method of vertically aligning pure carbon nanotubes by low temperature thermal chemical vapor deposition with direct current (DC) bias, by which high-quality carbon nanotubes for field emission display (FED) are deposited on a large area silicon or glass substrate at a low temperature to have a large area.
2. Description of the Related Art
Carbon nanotubes, which receive much attention of late, are hollow, long in length in contrast to a short diameter of several tens of nm, and stable chemically and dynamically in structure. Thus, carbon nanotubes are used to form electron emission tips for FED.
Carbon nanotubes are recommended to be vertically aligned and grown on a large substrate to be used as an FED electron emission tip material. In the prior art, screen printing has been used to vertically align carbon nanotubes, but there is difficulty in evenly distributing or vertically aligning carbon nanotubes.
At present, attempts to solve the above problem by growing carbon nanotubes directly on a substrate to be vertically aligned have been actively carried out. If carbon nanotubes can be vertically aligned on a glass substrate to have a large area, they can be applied directly to FEDs, thereby lowering a turn-on voltage and reducing the production costs due to a cut in process steps.
The above problem can be solved by a carbon nanotube growing method using a thermal chemical vapor deposition technique in which carbon nanotubes are grown on a substrate using hydro-carbon carbide gas such as CH4, C2H2, C2H4 or C2H5OH at a high temperature. However, according to this method, the growth temperature of carbon nanotubes is high at 900xc2x0 C. or greater.
Alternative to the above method is a method of lowering the growth temperature by depositing a transition metal on an Si or glass substrate to form a nuclear grain and also bring about catalysis. However, even in this alternative, there is difficulty in obtaining high-quality uniform carbon nanotubes at a low temperature of 600xc2x0 C. or less over a large area. In a chemical deposition method using plasma, the growth temperature can be lowered by a certain degree, but there is difficulty in obtaining carbon nanotubes over a large area.
According to techniques known up to now, carbon nanotubes can be grown on a substrate of up to 2xe2x80x3 inches at a growth temperature of about 660xc2x0 C. using a thermal chemical vapor deposition apparatus. Also, carbon nanotubes are successfully obtained at a low temperature of 550xc2x0 C. or less by a catalytic reaction caused by a palladium transition metal plate installed around the surface of a substrate on which carbon nanotubes are to be grown. However, there are drawbacks such as bad uniformity and generation of defective non-aligned carbon nanotubes. Also, since there are carbonaceous particles not changed into carbon nanotubes, carbon nanotubes cannot be directly used as an FED electron emission material.
To solve the above problems, an objective of the present invention is to provide a method of growing high-quality carbon nanotubes for field emission display (FED) on a silicon or glass substrate at a low temperature over a large area by solving the difficulty of a conventional thermal chemical vapor deposition apparatus in growing carbon nanotubes at a low temperature.
To achieve the above objective, the present invention provides a thermal chemical vapor deposition method to vertically align carbon nanotubes on a substrate using hydro-carbon gases, the method including, (a) catalytically thermally decomposing the hydrogen carbide gas at a temperature no greater than 600xc2x0 C. by passing the hydro-carbon gases through a mesh which is made of Ni, Fe, Co, Y, Pd, Pt, Au or an alloy of two or more of these materials or on which Ni, Fe, Co, Y, Pd, Pt, Au or an alloy of two or more of these materials is deposited; and (b) decomposing catalytically- and thermally-decomposed hydro-carbon gases by applying DC voltage to the space between a carbon nanotube growing substrate and an electrode substrate which is made of Ni, Fe, Co, Y, Pd, Pt, Au or an alloy of two or more of these materials or on which Ni, Fe, Co, Y, Pd, Pt, Au or an alloy of two or more of these materials is deposited.
Preferably, the hydro-carbon gases are methane, ethylene, acetone or propane, and the DC voltage is applied in a state where the carbon nanotube growing substrate is separated several mm apart from the electrode substrate.
Preferably, Ni, Fe, Co, Y, Pd, Pt, Au or an alloy of two or more of these materials is deposited on the electrode substrate or the carbon nanotube growing substrate by RF magnetron sputtering or electron beam evaporation, after Ti or TiN is deposited.
Preferably, several electrode substrates and an equal number of carbon nanotube growing substrates are mounted on an electrode substrate holder and a carbon nanotube growing substrate holder, respectively, and the DC voltage is applied to the space between the electrode substrates and the carbon nanotube growing substrate via a feedthrough. Also, it is preferable that the pressure within a reaction chamber is lowered to several motor during growing the carbon nanotubes.
Preferably, the carbon nanotube growing substrate is pre-treated using NH3 gas before the carbon nanotubes are grown.